What is the effect of temperature changes on the viscosity stability of cellulose ether in building materials? ​

Temperature changescellulose etherThe viscosity stability of building materials such as hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, etc. is significantly affected in building materials such as cement mortar, putty, coatings, etc. The core mechanism is related to the molecular chain movement state, hydrogen bonding, and system compatibility. The following provides a detailed analysis from the perspectives of temperature increase and decrease:

1、 The Effect and Mechanism of Temperature Rise on the Viscosity Stability of Cellulose Ether

In the application of building materials, an increase in temperature usually leads to a decrease in the viscosity of cellulose ether solution, but the degree of decrease varies depending on the type of cellulose ether, degree of substitution, and system environment (such as salt and pH). The specific manifestations and mechanisms are as follows:

The stretching state of the molecular chain is disrupted

The hydroxyl groups (- OH) and etherification groups (such as - OC ₂ H ₅, - OCH ₂ COOH) on the cellulose ether molecular chain combine with water molecules through hydrogen bonding in water to form a stable network structure, which is the core of its thickening ability. When the temperature increases, the thermal motion of molecules intensifies, hydrogen bonds are weakened or even broken, and the originally stretched molecular chains contract and curl due to thermal disturbance, resulting in a loose network structure and a decrease in solution viscosity.

For example, hydroxyethyl cellulose (HEC) can form a high viscosity solution at room temperature, but at temperatures above 80 ℃, hydrogen bonding is significantly disrupted, and viscosity can decrease by more than 50%, affecting the water retention and thixotropy of cement mortar.

The correlation between temperature resistance and degree of etherification

The type and degree of substitution of etherification groups (the number of hydroxyl groups etherified on each glucose unit) determine the temperature resistance of cellulose ethers:

Cellulose ethers with high degree of substitution (such as methyl cellulose MC, with a degree of substitution DS of 1.5~2.0) have enhanced hydrophobicity, more stable intermolecular interactions, and a smaller decrease in viscosity at high temperatures;

Cellulose ethers with low degree of substitution (such as some carboxymethyl cellulose CMC) are more susceptible to the thermal motion of water molecules at high temperatures due to their strong hydrophilicity, resulting in poor viscosity stability.

Synergistic effects with other components in the building materials system

Building materials often contain components such as cement, gypsum, sand and gravel, and their hydration reactions release heat (such as cement hydration releasing heat, causing the system temperature to rise to 50-70 ℃). High temperature may intensify the interaction between cellulose ether and calcium ions (Ca ² ⁺) and magnesium ions (Mg ² ⁺):

partcellulose etherThe carboxyl group of (such as CMC) will combine with Ca ² ⁺ to form a precipitate, disrupting the thickening network of molecular chains, resulting in a sudden drop in viscosity and affecting the flowability and water retention of mortar.

2、 The Effect and Mechanism of Temperature Reduction on the Viscosity Stability of Cellulose Ether

When the temperature decreases, the viscosity of cellulose ether solution usually increases, but excessive low temperature may lead to gel or delamination, and damage the stability. The specific performance and mechanism are as follows:

Molecular chain motion slows down, hydrogen bonding strengthens

At low temperatures, molecular thermal motion weakens, the hydrogen bonds between cellulose ether chains and water molecules become more stable, the degree of chain stretching increases, and the network structure becomes denser, resulting in an increase in solution viscosity. This change may manifest in building materials construction as:

The flowability of cement mortar or putty decreases at low temperatures (such as 5-10 ℃), and the mixing resistance increases, requiring additional adjustment of water volume to ensure workability.

Low temperature gel phenomenon (for specific cellulose ether)

Some cellulose ethers (such as methyl cellulose MC and hydroxypropyl methyl cellulose HPMC) have "thermosetting property" - they dissolve in water at low temperature to form a solution with high viscosity, and suddenly precipitate and form gel when the temperature rises to a certain threshold (gel temperature, usually 50~70 ℃); However, excessive low temperature (such as below 0 ℃) may lead to water molecule crystallization, disrupt the compatibility between cellulose ether and water, and instead cause molecular chain aggregation, stratification, or precipitation, resulting in abnormal viscosity fluctuations (first increasing and then decreasing).

For example, during winter construction, if the temperature of the building material system is below 0 ℃, HPMC may lose its thickening effect due to water freezing, resulting in a decrease in water retention and easy cracking of the mortar.

3、 The actual impact and countermeasures under different building material scenarios

Cement mortar/concrete

High temperature (such as summer construction or hydration heat release): The viscosity of cellulose ether decreases, which may lead to insufficient water retention and bleeding (water separation) of mortar, affecting strength and workability.

Low temperature (such as winter construction): the increase of viscosity leads to poor liquidity, and the risk of gel increases, which may lead to hollowing and cracking.

Response: Choose cellulose ether with high degree of substitution and strong temperature resistance (such as HPMC), or compound a small amount of retarder (to reduce the hydration heat release rate) and air entraining agent (to improve low-temperature fluidity).

Wall putty/coating

High temperature: The decrease in coating viscosity can easily lead to sagging (flowing downwards after painting), and putty is prone to rapid drying and powdering due to insufficient water retention.

Low temperature: Difficulty in mixing putty, slow film-forming speed of coatings, and possible decrease in adhesion due to slow evaporation of water.

Response: Adjust the amount of cellulose ether (increase it appropriately at high temperature and decrease it appropriately at low temperature), or add antifreeze (such as ethylene glycol) to control the low-temperature gel.

summary

Temperature changes affectcellulose etherThe hydrogen bonding, stretching state and compatibility with water molecules of molecular chains directly lead to the fluctuation of viscosity stability in the building materials system: high temperature reduces the viscosity (hydrogen bond destruction), low temperature increases the viscosity (hydrogen bond enhancement), and special temperature (too high or too low) may lead to abnormal phenomena such as gel and delamination. In practical applications, it is necessary to select cellulose ether types that match temperature resistance according to the construction environment temperature (such as HPMC being superior to ordinary MC), and alleviate the negative effects of temperature fluctuations through formula adjustments (such as dosage and compound additives) to ensure the construction and performance of building materials.